“Data center energy usage has risen dramatically over the past decade and will continue to grow in-step with the processor-intensive applications that support business and day-to-day life in the modern world. The growth of technology has driven the data center into a new phase of expansion, and while data centers themselves may vary over different industry segments, there are common factors influencing all of them including a need to do more with the same resources, or in some cases, even less. To this end, much has been done to increase server efficiency and IT space utilization, but the actual space and cooling infrastructure supporting these intensified loads has often not been properly addressed to keep pace with these developments—an important oversight since cooling can represent up to 42% of a data center's energy usage.”
Daniel Kennedy, Rittal White Paper 507: Understanding Data Center Cooling Energy Usage & Reduction.
Available Cooling Systems
Over the years, many methods have been used to cool IT loads in the Data Center environment. The master table below lists some methods commonly used in the industry. These products are available from various manufacturers—some have been available for quite some time and others have just recently been introduced. The table is not a complete list of vendors, but is intended as a reference for some of the most commonly deployed systems.
Table 1 illustrates energy usage by evaluating the energy required to operate the system in kilowatts (kW) versus the cooling capacity provided in tons of cooling/refrigeration (12,000 BTU/hr is equivalent to 1 ton of refrigeration)—a kW/ton rating.
TABLE 1Commonality in theAvailabilityManufacturersIndustryCRAC Cooled System30+YearsLiebert, DataAire,Very CommonStultzCRAH Cooled System30+YearsLiebert, DataAire,Very CommonStultzCRAC Cooled System5-10yearsThe above for CoolingGaining Wide-W/Containmentunits; containmentspread Acceptancefrom Rittal, CPI,Polargy, APC, KnurrCRAH Cooled System5-10yearsThe above for CoolingGaining Wide-W/Containmentunits; containmentspread Acceptancefrom Rittal, CPI,Polargy, APC, KnurrLiquid Cooled Rack8yearsRittal, APC, Knurr,CommonUnoptimizedLiebert, HPLiquid Cooled Racks8yearsRittal, HP, KnurrLess CommonChilled Water TemperatureOptimizedLiquid Cooled Racks8yearsRittal, HP, KnurrLess CommonChilled Water TemperatureOptimized andFree Cooling SystemsLiquid Cooled Racks8yearsRittal, HP, KnurrLess CommonChilled Water TemperatureOptimized andEvaporative Free CoolingSystemsActive Liquid Cooled5yearsRittalLess CommonDoors, Chilled WaterTemperature Optimizedand EvaporativeFree Cooling SystemsPassive Liquid Cooled8yearsRittal, IBM, VetteLess CommonDoors Chilled WaterTemperature Optimizedand EvaporativeFree Cooling SystemsPumped Refrigerant5yearsLiebertLess CommonSystemsAir Side Economizing30+YearsCustom EngineeredCommonSolutions with componentsfrom variousprovidersLiquid Cooled Servers30+YearsOriginally used inRaremainframes, but proposed100% heat removalvery rare, closestmanufacturerwould be SprayCool
Typical Data Center cooling is accomplished using standard HVAC techniques. That is, the whole building is cooled just as any other building is cooled using supply and return air ductwork, under-floor air distribution space, air inlets, air outlets, etc. Primarily, the air is conditioned at a small number of locations and then moved through ductwork and/or via under-floor air distribution space to a desired outlet location. Once expelled from the outlet, the cooled air mixes with room air. Eventually, the room air enters a server rack where it picks up heat from the servers and the hot air is expelled back into the room where it again mixes with room air. In some slightly more sophisticated systems, the server racks are arranged into aisles, which do a better job of segregating warmed air from cooled air. But in most cases, heat is generated far from the location of the room temperature controllers and far from where heat is removed. This distance causes a big thermal lag or inertia in the system and requires that some areas be over cooled to insure sufficient cooling building wide. This wastes energy. The following table provides data about the capacity, operation; CAPital EXpenditures (CAPEX) and OPerating cost EXpenditures (OPEX) of typical Data Centers where even the oversized cooling systems are unable to provide the required cooling to the all IT Room server rack enclosures.
Data Center LOST capacity is the inability to convert the intended design loading capacity into operational reality, or in other words, resources are not fully utilized. Changes to the Data Center capacity roadmap, i.e. increased Rack load densities, which fail to conform to initial design and design assumptions results in lost capacity. Data Center capacity is LOST when changes from the original design causes space, power, COOLING, or network to become unavailable to the IT equipment. For example, if Rack densities increase from 4 KW per Rack to 8 KW per Rack, the IT load in the average enterprise Data Center is increased from 1×KW to 2×KW, but the COOLING system was initially design for 1×KW plus, in some cases, 50% accounting for unexpected additional COOLING requirements or 1.5×KW. At an increased density to 2×KW per Rack, the Data Center will have to decommission 25% of its Racks reducing its Data Center Capacity by 25% due to lack of COOLING resources. Analysis shows an Annual Cost of Deployed Capital of $8,308 per KW related to Data Center CAPEX and OPEX resulting in substantial costs to the Data Center for loosing capacity due to lack of COOLING.
TABLE 2Lost Capacity and its Capital Cost to a Data CenterBased on Future Facilities White Paper “The Elephant in the Roomis Lost Capacity” and the Uptime Institute Analysis of 1.3 MWData CenterMWs1.3KWs1300Annualized CAPEX $6,300,000Annualized OPEX $3,100,000Load Dependent OPEX $1,400,000Total Annual Capital Deployed$10,800,000Total Annual Capital Deployed per KW   $8,308Lost Capacity - 20% for 1 year and for 5 $2,160,000$10,800,000yearsLost Capacity - 30% for 1 year and for 5 $3,240,000$16,200,000yearsLost Capacity - 40% for 1 year and for 5 $4,320,000$21,600,000years
What is needed is a system of cooling server racks or electronics enclosures that more closely places cooling means near the heat load of the server and which is capable to provide real time cooling for an individual server rack or electronics enclosure based on its load demand.